rust: fix musl build

[ci skip]

srcpkgs/rust/files/musl.patch

@@ -1,11 +1,11 @@
---- rustc-1.28.0-src/src/librustc_target/spec/x86_64_unknown_linux_musl.rs.orig	2018-08-08 23:21:51.673454236 +0200
-+++ rustc-1.28.0-src/src/librustc_target/spec/x86_64_unknown_linux_musl.rs	2018-08-08 23:23:11.080834122 +0200
-@@ -11,7 +11,7 @@
- use spec::{LinkerFlavor, Target, TargetResult};
-
- pub fn target() -> TargetResult {
--    let mut base = super::linux_musl_base::opts();
-+    let mut base = super::linux_base::opts();
-     base.cpu = "x86-64".to_string();
-     base.max_atomic_width = Some(64);
-     base.pre_link_args.get_mut(&LinkerFlavor::Gcc).unwrap().push("-m64".to_string());
+Reason: https://gist.github.com/ab75b3796a9383423deecc0828494ac5
+--- rustc-1.28.0-src/src/librustc_target/spec/linux_musl_base.rs.orig   2018-10-08 21:02:21.588611506 +0200
++++ rustc-1.28.0-src/src/librustc_target/spec/linux_musl_base.rs        2018-10-08 21:02:40.846454873 +0200
+@@ -61,7 +61,7 @@
+     base.post_link_objects_crt.push("crtn.o".to_string());
+
+     // These targets statically link libc by default
+-    base.crt_static_default = true;
++    base.crt_static_default = false;
+     // These targets allow the user to choose between static and dynamic linking.
+     base.crt_static_respected = true;

srcpkgs/rust/template

@@ -155,7 +155,7 @@ do_configure() {
 	fi
 	case "$XBPS_TARGET_MACHINE" in
 	*-musl)
-		configure_args+=" --musl-root=/usr"
+		configure_args+=" --set=target.${_host_triplet}.musl-root=/usr"
 		;;
 	esac